Scientists are now having their day in the Sun… a day that will last 8 years.

In October 2006, NASA launched a pair of twin spacecraft into space. Called STEREO — Solar TErrestrial RElations Observatory — they traveled in opposite directions, one ahead and the other behind the Earth in its orbit around the Sun. The goal was to get a wide, stereoscopic view of the Sun which would provide 3D information on our star.

Today they reached that goal. After traveling a combined 470 million kilometers (290 million miles) relative to the Earth, they are now on opposite sides of the Earth’s orbit, staring down at opposing faces of the Sun.

This image [click to ensolenate], taken just four days ago, is the result: the far side of the Sun! If you could bore straight through the center of the Sun in this image, plunging through nearly 1.4 million kilometers of solar fire, out the other side, and straight on for another 150 million kilometers, you’d be back at the Earth.

Mind you, the STEREO spacecraft reached their 180° separation today, and this image was taken just before that happened. The black line represent the small amount of solar real estate still invisible to the twin probes last week, but which can now be seen (I expect we’ll get that image from NASA pretty soon). The images are slightly fuzzy around that line because to the two spacecraft that’s the edge of the Sun where their view is distorted by perspective. However, that’s a minimal issue, and this is the first time we’ve ever seen the actual entire far side of the Sun!

I’ll note that there is no real, permanent far side of the Sun like there is for the Moon. The Moon spins once for every time it goes around the Earth, so it appears like the same face is always toward us. But the Sun rotates once about every 24.5 days. During that time, the Earth has moved 1/15th of the way around its orbit, so the Sun has to spin a little more to "catch up" with the Earth — another 1.7 days. So over the course of about a month we see the entire surface of the Sun.

But during that time it’s changing. The Sun is not a solid object; it’s a seething, writhing ball of plasma (ionized gas). Something might happen on the far side and it would take a week or more for it to rotate into view, and by then it will have evolved or possibly even disappeared entirely!

That’s no longer a problem. From their perches 1/4 of the way around the Sun each, STEREO will see anything that happens on the Sun’s far side, and scientists now have, for the first time, a 360° view of the entire solar surface. NASA has created a short video to explain all this:

Scientifically, this is critical for understanding the Sun. Events that happen anywhere on the Sun can have a ripple effect everywhere else… literally. A solar flare is a vast explosion on the Sun’s surface, releasing as much energy in a few minutes as millions or even billions of nuclear bombs. This sends gigantic seismic waves, ripples, across the Sun’s surface, affecting other regions. Gigantic coronal mass ejections (CMEs) are like hurricanes over the Sun, and the region causing one can extend onto the far side of the Sun where we can’t see it. Solar prominences and other features can be huge, stretching across the face of the Sun, again hiding part from view.

And, of course, in astronomy more is better. Having a better view, a better vantage point, just plain ol’ more data, is a big help. One thing astronomers have learned over the years is that new views provide new insights. Opening your eyes a little wider is always a good thing.

And this view will last for some time. The two spacecraft can’t suddenly stop and hover over the Sun; they are still moving around it, away from Earth. Eventually they’ll pass each other on the other side of the Sun, and start moving apart again, having swapped sides. However, we have the Solar Dynamics Observatory orbiting us here, providing a view of the near side of the Sun, so we’ll still have 360° solar coverage for the next eight years!

The Sun affects every aspect of life on Earth, from our light and heat to how flares and CMEs can potentially damage satellites and cause blackouts on the ground. We need to study this star, understand it. I want to know more just for the joy of learning, but in this case the science returned from missions like STEREO have a profound importance for all of us.

@Jeffersonian, Werdna and others… watch the video, that’ll explain it for you. (If you consider the Earth to be at 6:00, the STEREO craft are currently at 3:00 and 9:00. In 2015 they’ll pass each other at the 12:00 position, then move on to the opposite 9:00 and 3:00 spots before we lose the full 360 degree view in 2019. Maybe we’ll launch more craft in 4 years? As the craft orbit towards each other, we’ll have a “stereoscopic view” of the far side as we did the near side on their way out.)

Phil said: “The goal was to get a wide, stereoscopic view of the Sun which would provide 3D information on our star. ”

I don’t know if this was the/a goal.
But if it was then it will be realised when ever either of the satellites is at the correct angle for stereo imagery from the other or from the earth.
This will occur sometime after launch, again sometime before they cross behind the sun, again after they cross behind the sun and again as they re-approach earth.

The cycle will then repeat for as long as they maintain their orbits and comms.
(Warning: This is all supposition )

That big orange thing kicks out more energy in 1 second than has been used in all of human history, it loses 4 million tonnes of material into space every second, and a photon takes a few hundred thousand years to get from the core to escape from the surface as light.

Another stupendous fact is it’s a massive 99.86% of all the mass in the solar system.

Once they pass directly behind the sun, how will they send images back? I’d imagine the sun would somewhat obscure any electromagnetic waves passing through it…though I suppose if anything did make it through, it would be interesting to see exactly how it was affected.

Eventually they’ll pass each other on the other side of the Sun […] What if they don’t pass each other, but, well, exchange greetings and metal? Maybe they add a bit of metallicity to the sun!

I’d like them when they get close enough to take their cameras off our Sun -just for a second or ten – and photograph *each other* flying by like spaceships in the night. How neat would that be?! 8)

Of course it may well be that they’ll still be too far apart for this. Space – even on similar orbits – is very big indeed. [Insert obligatory Hitchhikers Guide to the Galaxy quote here.] Still, I wonder ..

Surely the image he has posted up isn’t from looking directly at two images taken from the two STEREO satellites. If that was the case the dark area of missing information would be around one side of the periphery of the image.

Surely, what NASA has done is manipulate the images, so that what was on the periphery is now central.

I think that this is an image of the sun you would get if you were 180 degrees around the orbit from the satellites, not an image of what they are directly seeing. I am right in this surmise?

A further confusion for me is that Phil says ” If you could bore straight through the center of the Sun in this image, plunging through nearly 1.4 million kilometers of solar fire, out the other side, and straight on for another 150 million kilometers, you’d be back at the Earth.”

Is this saying that when the two Stereo satellites are 180 degrees apart, they are also 180 degrees around from the earth?

Is that a coincidence, or some amazing gravitational affect which has made this conjunction of the satellites possible.

If he’d said you’d be back at the other satellite I’d still be confused, because of my understanding that this isn’t an image of what each satellite is directly seeing – if that was the case then if you went through the image you would end up at the other satellite. But that can’t be what this image is, or else the black line would be on the periphery not in the center of the image.

Am I correct in all this?

Anyway, its an amazing image, but unfortunately it seems my understanding of it, is different from what Phil is saying. Or else maybe I’m just not understanding.

I’d only suggest that its not only NASA that has delivered such cool results. There was significant UK involvement in the design & build, and we’re managing instruments on the mission, too. Check it out – http://www.ukspaceagency.bis.gov.uk/22025.aspx

Neil Taylor @ #31 asked: “I am a little confused by what Phil has said in this post. Surely the image he has posted up isn’t from looking directly at two images taken from the two STEREO satellites. If that was the case the dark area of missing information would be around one side of the periphery of the image. Surely, what NASA has done is manipulate the images, so that what was on the periphery is now central.”

That’s correct. As you look at that image, the two satellites are off screen to left and right. As *they* see the Sun, the parts of their images which are on the edge are what we see down the middle – hence the blurring.

“I think that this is an image of the sun you would get if you were 180 degrees around the orbit from the satellites, not an image of what they are directly seeing. I am right in this surmise?”

No, what we see is 90 degrees around from each satellite.

“A further confusion for me is that Phil says ” If you could bore straight through the center of the Sun in this image, plunging through nearly 1.4 million kilometers of solar fire, out the other side, and straight on for another 150 million kilometers, you’d be back at the Earth.” Is this saying that when the two Stereo satellites are 180 degrees apart, they are also 180 degrees around from the earth?”

No. As mentioned above, the two satellites are off screen to left and right. They’re both 90 degrees around the Sun from the Earth, and this image is created as though we’re 90 degrees from the satellites and 180 degrees around from the Earth. If you were looking down at this scene from above, the Earth is at 12 o’clock, the satellites are at 3 o’clock and 9 o’clock, and this image is created as though the viewer was at 6 o’clock.

“Is that a coincidence, or some amazing gravitational affect which has made this conjunction of the satellites possible.”

No, they were deliberately sent off in opposite directions around the Sun. At some point they’re going to be on opposite sides of the Sun.

“If he’d said you’d be back at the other satellite I’d still be confused, because of my understanding that this isn’t an image of what each satellite is directly seeing – if that was the case then if you went through the image you would end up at the other satellite. But that can’t be what this image is, or else the black line would be on the periphery not in the center of the image. Am I correct in all this?”

As mentioned above, this is an image created by manipulating images taken by satellites on opposite sides of the Sun. We have software which can take an image which is known to be projected onto a sphere and rotate it so that we can what it would look like from different angles.

A similar thing was done for real in the early days of the Apollo program: astronomers took the best image they had of the Full Moon and projected it onto a giant sphere. They discovered that a feature near the Moon’s South Pole which barely registered in the photo was actually a massive basin.

“Anyway, its an amazing image, but unfortunately it seems my understanding of it, is different from what Phil is saying. Or else maybe I’m just not understanding. Can anyone clarify?”

Ensolenate – (v.i.) 1) A verb contrived by scientists trying to elevate the importance of the obvious. i.e. “These low resolution pics of the sun with wildly distorted artifacts at the periphery of the spacecraft’s vision would appear much more relevant if the user would have an option to ‘ensolenate’ them.”

Probably a testament to the fact that I have kids that I thought of Phineas and Ferb’s Dr. Doofenshmirtz trying to eliminate the full moon by rotating the moon so the dark side would always face Earth.

Oh, I see. The light from the moon is just the reflection off the sun! Dummkopf! I should have rotated the sun.

Dotan Cohen: How is it that the satellites are more or less 1 AU from the Sun, but they orbit faster than the Earth? Shouldn’t orbiting the Sun faster than the Earth require a smaller orbital radius?

Yes, but if you’re patient (which NASA certainly has to be) the difference in orbital radius can be very small. So for instance, for the one that’s “ahead” of earth, you make a small burn retrograde to your orbit around the sun (yeah, you “slow down” to “speed up” 😛 ) and the point where you made the burn is now the aphelion of your orbit (the part that’s furthest from the sun). So you wait, say, 2 years, while your smaller orbit takes you “ahead” of the earth, and then you make a small prograde burn which brings your orbital radius back up to that of the earth. The one “behind” the earth does things the opposite way – prograde burn to raise the other end of their orbit beyond that of the earth, some waiting, then a retrograde burn at the right time (to match earth’s orbit again, it’s most efficient if they wait until they’re back at the same point where they made the original burn).

If you ever have a chance, try the free space simulator Orbiter (google orbitersim). It’s got a bit of a learning curve, but you can pilot spacecraft and watch your orbit projected in realtime on your instruments as you perform burns. It makes basic orbital maneuvers (that are kinda hard to visualize from reading about them) relatively intuitive